# Central Venous Pressure (CVP) — Anaesthesia Notes

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## 1. Definition

**Central Venous Pressure (CVP)** is the blood pressure measured in the superior vena cava or right atrium. It approximates **right atrial pressure (RAP)** and therefore serves as an index of:

- Right ventricular preload
- Circulating blood volume
- Venous tone
- Right ventricular performance

> Normal CVP: **2–8 mmHg** (supine, at rest)

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## 2. Physiological Basis

CVP reflects the balance between venous return to the right heart and the ability of the right ventricle to eject that volume. It is influenced by:

| Factor | Effect on CVP |
|--------|---------------|
| Hypovolaemia | ↓ CVP |
| Hypervolaemia | ↑ CVP |
| Right heart failure | ↑ CVP |
| Cardiac tamponade | ↑ CVP |
| Tension pneumothorax | ↑ CVP |
| PEEP / high intrathoracic pressure | ↑ CVP |
| Vasodilation (sepsis, anaesthesia) | ↓ CVP |
| Tricuspid regurgitation | ↑ CVP (ventricularised waveform) |

> **Key limitation**: CVP reflects **right-sided** heart function, NOT left ventricular performance.

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## 3. Indications for CVP Monitoring / CVC Insertion

*(Miller's Anaesthesia, 10e — Box 32.5)*

### Monitoring indications
- CVP and haemodynamic monitoring in unstable patients / major surgery
- Pulmonary artery catheterisation
- Transvenous cardiac pacing

### Access indications
- Infusion of vasoactive drugs (adrenaline, noradrenaline, vasopressin)
- Hyperalimentation / total parenteral nutrition (TPN)
- Chemotherapy or agents irritating to peripheral veins
- Prolonged antibiotic therapy (e.g., endocarditis)
- Rapid fluid resuscitation via large-bore introducer sheath
- Trauma or major surgery
- Aspiration of venous air emboli
- No adequate peripheral IV access
- Repeated blood sampling

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## 4. Access Sites

| Site | Advantages | Disadvantages |
|------|-----------|---------------|
| **Right internal jugular (RIJ)** | Most direct route to RA/RV; highest success rate; preferred for pacing wire / PA catheter | Carotid artery risk; patient discomfort |
| **Left internal jugular** | Alternative when right unavailable | Longer to SVC (3–5 cm extra); thoracic duct risk |
| **Subclavian** | Patient comfort; lower infection risk | Higher pneumothorax risk — avoid in severe emphysema; difficult to compress if bleeding |
| **External jugular** | Easy in some patients | Kinks in lateral decubitus (problem during thoracotomy / OLV) |
| **Femoral** | Useful when neck immobilised (trauma) | Infection risk; catheter may not reach central circulation reliably |
| **Antecubital (PICC)** | Minimally invasive | Longer insertion; positional |

### Site selection principles
- **Coagulopathic patients** → internal or external jugular (compressible); avoid subclavian
- **Severe emphysema** → internal jugular (lower pneumothorax risk vs subclavian)
- **Emergency transvenous pacing** → right internal jugular (most direct route to RV)
- **Cervical collar / trauma** → femoral or subclavian approach

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## 5. Technique Essentials

- Use **real-time ultrasound guidance** — strongly recommended, especially for internal jugular (reduces complications, increases first-pass success)
- Use **maximal barrier precautions** (cap, mask, sterile gown, sterile gloves, full-body drape)
- **Seldinger technique**: needle → guide wire → dilator → catheter
- Confirm venous placement with **waveform manometry or pressure measurement** before use
- Verify catheter tip position on **chest X-ray** — tip should lie in SVC above the right atrial junction (within 2 cm of cardiac silhouette on AP CXR for PA catheter)

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## 6. CVP Waveform

### 6.1 Normal Waveform Components

*(Miller's Anaesthesia 10e — Table 32.3)*

| Component | Phase | Mechanical Event | ECG Timing |
|-----------|-------|------------------|------------|
| **a wave** | End-diastole | Atrial contraction ("atrial kick") | After P wave |
| **c wave** | Early systole | Isovolumic ventricular contraction; tricuspid valve bulges into RA | End of QRS |
| **x descent** | Mid-systole | Atrial relaxation + descent of tricuspid annulus toward apex | Before T wave |
| **v wave** | Late systole | Venous filling of atrium while tricuspid is closed | End of T wave |
| **y descent** | Early diastole | Tricuspid valve opens; blood flows RA → RV | Before P wave |
| **h wave** | Mid-to-late diastole | Diastolic plateau (only seen at slow HR or elevated CVP) | — |

**Mnemonic**: a = Atrial contraction; c = Closure of tricuspid; x = eXit of blood (atrial relaxation); v = Venous filling; y = Yield to ventricle

> CVP is read at the **base of the c wave at end-expiration** (Fishman's Pulmonary, 5e)

### 6.2 CVP Waveform Image

![CVP waveform with ECG correlation — a, c, x, v, y components labelled](https://cdn.orris.care/cdss_images/3b2b9eed00a8df26b799d84f99f2ba0834a16fcd6e432c3df80e8366817047d7.png)

*CVP waveform with simultaneous ECG. The a wave follows the P wave; the c wave follows the QRS; the v wave peaks after the T wave.*

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## 7. CVP Waveform Abnormalities

*(Miller's Anaesthesia 10e — Table 32.3 Abnormalities)*

| Condition | Waveform Change | Mechanism |
|-----------|----------------|-----------|
| **Atrial fibrillation** | Loss of a wave; prominent c wave | No organised atrial contraction |
| **AV dissociation / complete heart block** | Cannon a waves | Atrium contracts against closed tricuspid |
| **Tricuspid regurgitation** | Tall systolic c-v wave; loss of x descent ("ventricularised" waveform) | Regurgitant systolic filling of RA |
| **Tricuspid stenosis** | Tall a wave; attenuated y descent | Impaired diastolic emptying of RA |
| **Cardiac tamponade** | Dominant x descent; attenuated y descent ("x without y") | Equalised pressures; impaired RA filling in diastole |
| **Pericardial constriction** | Tall a and v waves; steep x AND y descents; M or W pattern | Impaired ventricular filling with exaggerated pressure equalisation |
| **RV ischaemia / infarction** | Tall a and v waves; steep x and y descents; M or W pattern | Poor RV compliance |
| **Junctional rhythm** | Loss of a wave | No P wave → no organised atrial contraction |

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## 8. Measurement Technique

### Zeroing and levelling
- Zero reference point: **5 cm below the sternal angle** (uppermost fluid level in RA) OR **one-third of thoracic AP dimension** (mid-RA level)
- Commonly: mid-thoracic level (phlebostatic axis)
- Consistency throughout monitoring period is **most important**

### Respiratory variation
- Measure at **end-expiration** in both spontaneous and positive-pressure ventilation
- PEEP elevates CVP — account for this when interpreting values

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## 9. Clinical Interpretation

### CVP in shock

| Shock Type | Expected CVP |
|------------|-------------|
| Hypovolaemic | Low (↓) |
| Distributive (sepsis, anaphylaxis) | Low (↓) |
| Cardiogenic (right heart failure) | High (↑) |
| Obstructive (tamponade, tension pneumothorax, massive PE) | High (↑) |

> These are generalisations — CVP must be interpreted in the full clinical context.

### CVP and fluid responsiveness

**CVP is a POOR predictor of fluid responsiveness.** (Miller's Anaesthesia 10e; Barash Clinical Anaesthesia 9e)

- Multiple RCTs and systematic reviews show **very poor relationship between CVP and circulating blood volume**
- A single static CVP value **cannot predict** response to a fluid challenge
- **Dynamic variables are preferred** for guiding fluid therapy:
  - Pulse pressure variation (PPV)
  - Stroke volume variation (SVV)
  - Passive leg raise response
  - Oesophageal Doppler
  - Point-of-care echocardiography

> *"Consensus guidelines recommend against using static measures like CVP to assess the likelihood of fluid responsiveness, favouring use of dynamic variables."* — Fishman's Pulmonary Diseases and Disorders, 5e

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## 10. Complications of CVC Insertion

*(Miller's Anaesthesia 10e — Box 32.6)*  
Up to **15%** of patients may experience some adverse event.

### Mechanical
- **Arterial puncture** — most common acute complication (1.9–15%); can cause haematoma, AV fistula, pseudoaneurysm, or stroke (carotid)
- **Pneumothorax** — higher with subclavian approach; catastrophic if in dependent lung during OLV
- **Haemothorax / hydrothorax / haemomediastinum**
- **Chylothorax** (left subclavian / left IJ — thoracic duct injury)
- **Air embolism** — risk during insertion (Trendelenburg position reduces risk)
- **Catheter malposition** — tip in wrong vessel or chamber
- **Arrhythmias** — guide wire irritation of RV/RA

### Thromboembolic
- **Deep vein thrombosis** — especially femoral and subclavian sites
- **Pulmonary embolism**
- **Catheter-related thrombosis**

### Infectious
- **Central line-associated bloodstream infection (CLABSI)** — significant cause of ICU morbidity/mortality
- Prevention: maximal barrier precautions, chlorhexidine skin prep, standardised insertion checklists, daily review of necessity

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## 11. Specific Anaesthetic Contexts

### Thoracic surgery / pneumonectomy
- CVP catheter commonly placed for oesophagectomy and pneumonectomy
- **Avoid subclavian approach** — pneumothorax risk in dependent lung during OLV is catastrophic
- **External jugular should be avoided** during thoracotomy — kinks when patient turned to lateral decubitus
- CVP no longer considered accurate guide for fluid responsiveness in thoracic surgery
- *(Barash Clinical Anaesthesia 9e)*

### Cardiac surgery / haemodynamically unstable patients
- CVP used alongside other haemodynamic monitors (PA catheter, TOE)
- PA catheter placed through right IJ via the CVC site
- Characteristic pressure waveforms confirm passage through RA → RV → PA → wedge position

### Transvenous pacing emergencies
- **Right internal jugular** preferred — most direct route to RV

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## 12. Summary — Key Points for Exams

1. CVP = right atrial pressure ≈ RV preload (NOT LV preload)
2. Normal: **2–8 mmHg**; measured at **end-expiration** at the **base of the c wave**
3. CVP waveform: **a, c, v** waves and **x, y** descents — timed against ECG
4. **Cannon a waves** = AV dissociation; **loss of a wave** = AF; **c-v fusion + loss of x** = tricuspid regurgitation
5. **CVP is a poor predictor of fluid responsiveness** — dynamic variables are preferred
6. **Right internal jugular** = preferred site for pacing wires and PA catheters
7. **Subclavian** has highest pneumothorax risk — avoid in emphysema and OLV cases
8. Complications: arterial puncture, pneumothorax, CLABSI, arrhythmias, air embolism
9. Always use **ultrasound guidance** (strongly recommended for IJ)
10. Waveform abnormalities are diagnostically useful — especially tamponade (dominant x, absent y) vs. constriction (steep x AND y)

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*Sources: Miller's Anaesthesia 10e (Elsevier); Barash, Cullen & Stoelting's Clinical Anaesthesia 9e; Fishman's Pulmonary Diseases and Disorders 5e; Morgan & Mikhail's Clinical Anaesthesiology 7e*